Automated change-speed transmissions can usually be operated both in an automatic mode with automatic initiation of gearshifts and in a manual shift mode with manual initiation of gearshifts. The engagement and disengagement of gears and the engagement and disengagement of the separating clutch take place, in each case, automatically by corresponding actuation of associated gear and clutch control elements, which are preferably in the form of hydraulic or pneumatic control cylinders or of electric motors. Various shifting devices, with different possible ways of actuating a selector lever, have become known for the manual selection of the automatic drive steps and the manual initiation of gearshifts.
A typical embodiment of a shifting device of an automated transmission is described, for example, in DE 38 07 881 C2. This known shifting device comprises an automatic shift gate extending in the longitudinal direction of the vehicle, in which the selector lever can be moved to drive-position P, for engaging the parking lock, drive-position R, for engaging the reversing gear, the neutral position N, drive-position D, for the automatic shift initiation of forward gears, and drive-positions 3, 2, 1 for the automatic initiation of forward gears with an upshift limitation. In addition the shifting device, has a manual shift gate extending parallel to the automatic shift gate, into which the selector lever can be moved, by being pivoted transversely, from a drive-position D of the automatic shift gate. Within the said manual shift gate, the selector lever is held by springs in a neutral central position. By moving the selector lever within the manual shift gate in the direction of a “+” position, arranged forward in the driving direction, an upshift, and in the direction of a “−” position, arranged rearward in the driving direction, a downshift can be initiated manually.
In another shifting device illustrated only schematically in EPO 467 773 B1, the neutral, central position marked M of the selector lever of a manual shift gate orientated transversely to the driving direction is located within the automatic shift gate that extends in the driving direction, between drive-position D for the automatic shift initiation of forward gears and an upshift-limiting stage 1. By moving the selector lever within the manual shift gate toward a “+” position on the right, relative to the driving direction, an upshift, and toward a “−” position on the left, relative to the driving direction, a downshift can be initiated manually.
In a shifting device known from DE 197 36 406 B4, the drive-position D of the automatic shift gate forms, at the same time, the neutral, central position of a fictive manual shift gate. In a first embodiment of this shifting device, an upshift can be initiated manually by a slight movement of the selector lever within the automatic shift gate toward a “+” position, arranged forward in the driving direction, and a downshift by a slight movement of the selector lever within the automatic shift gate toward a “−” position, arranged rearward in the driving direction. In a second embodiment variant of this shifting device, an upshift can be initiated manually by a slight movement of the selector lever within the D-position of the automatic shift gate toward the “+” position, arranged on the left relative to the driving direction, and a downshift by a slight movement of the selector lever toward the “−” position, arranged on the right relative to the driving direction.
From the motor vehicle “Smart Fortwo with Softip Shifting”, which has no automatic shift initiation for the engagement of forward gears, a shifting device is known in which the automatic shift gate is reduced to the neutral position N and the drive-position R for engaging the reversing gear. In the manual or ‘tip’ shift gate that runs parallel to the automatic shift gate, the selector lever can be moved, by a transverse pivoting, from the neutral position N of the automatic shift gate. In this shifting device, an upshift can be initiated manually by moving the selector lever within the manual shift gate from its neutral, central position toward a “+” position, arranged forward in the driving direction, and a downshift by moving it toward a “−” position, arranged rearward relative to the driving direction.
When the manual shift mode of the shifting device is actuated, i.e., when the selector lever is in the respective neutral, central position of the manual shift gate provided, operating situations can arise in which the motor vehicle is rolling with its drivetrain disengaged. The drivetrain is disengaged when the transmission is in its neutral position so that no gear is engaged, and/or the separating clutch is disengaged. Rolling with the drivetrain disengaged can occur during a starting process on an uphill or downhill stretch, and a distinction is made between rolling in the desired starting direction and rolling (rolling back) in the direction opposite to the desired direction.
When rolling at a relatively low travel speed, however, this may also result in rolling forward at a cross-road or at a red traffic-light. But rolling of the motor vehicle with the drivetrain disengaged can also take place at higher speeds, in particular when the motor vehicle is operated in a mode in which, when neither the accelerator pedal nor the brake pedal are actuated, at least the separating clutch disengages automatically and the motor vehicle concerned is allowed to roll with its drivetrain disengaged (also known as “coasting”). During traffic-related rolling ahead, at relatively low speed, and rolling in the coasting mode, at relatively high speed, the braking action of the drive motor otherwise present during a thrust operation is absent, which leads to fuel saving that can be increased still further by stopping the drive motor in the context of a start-stop operating mode.
However, regardless of its cause, rolling of the vehicle with its drivetrain disengaged is generally considered unsafe since, in such driving situation, the rolling or driving speed cannot be controlled by the driver using the accelerator pedal, as is otherwise usual, and the braking action of the drive motor that exists in a thrust operation is not available. Accordingly, in the corresponding drivetrains at least a control function is always provided by means of which, in the manual shift mode, rolling with an disengaged drivetrain can, when necessary, be ended by some appropriate control action by the driver, in particular by actuating the selector lever.
A control action that can be performed simply and quickly by the driver, for initiating a corresponding control sequence, consists in moving the selector lever just once out of the neutral, central position in the upshift direction, this also being provided in many automated transmissions. A corresponding control process of a motor vehicle drivetrain comprising a semi-automated transmission with a manual shift initiation is, for example, described in U.S. Pat. No. 5,664,458 A. This known method relates to the engagement of the drivetrain in a motor vehicle that is rolling with its drivetrain disengaged, such that provision is made for determining and engaging a starting gear, suitable for the actual rolling or travel speed, if a minimum speed is exceeded with the separating clutch disengaged.
On the other hand, from DE 102 21 701 A1 a method is known for controlling a motor vehicle drivetrain, during a so-called coasting operation of the said motor vehicle, in which the drivetrain is engaged by actuating the accelerator pedal or the brake pedal. With the transmission in neutral and the separating clutch disengaged, it is provided that after the signal to engage the drivetrain, the gear engaged before the drivetrain was disengaged, or at a higher vehicle speed even a higher gear is engaged, and the speed of the drive motor is matched to the speed of the transmission input shaft before the separating clutch is engaged.
A single movement of the selector lever in a particular shift direction during rolling can, however, also take place unintentionally by inadvertent touching of the selector lever by the driver or a front-seat passenger and, with a drivetrain controlled in accordance with the method of U.S. Pat. No. 5,664,458 A, this causes the drivetrain to engage in a manner that takes the driver by surprise and is undesired per se. Furthermore, if a vehicle is rolling at a higher speed in a coasting mode and the drivetrain is controlled in accordance with the method of DE 102 21 701 A1, even a relatively brief and slight actuation of the brake pedal will engage the drivetrain, although the driving situation may not require this and the driver does not wish it.